EIGRP Neighbor and Topology Table Explained

This topic is to discuss the following lesson:



You explain everything so clearly and everything look so simple.

Thank you so much.


Thank you so much for the breakdown. I went through two books that left me more confused than clarified.

it was really very helpful for me; i was confused to understand EIGRP Tables specially FD, AD etc; but explain it magically and you also remove all my misconceptions … Thanks and keep writing

Hi Rene. Very nice lesson which touches on the basics of eigrp topology table.
I have recently also written a blog which exposes few interesting things on the same topic.

This can be found here:

Hi Rafael,

Thank you. I just read your post, nice write-up!


this is the best site on the net. Please keep up the good work. I’m learning a lot from you.

Thanks Willie!

I read this lesson just for the revision but your way of explaining things in a proper structure is really amazing and too good thanks a lot and keep up the good work.

Thanks Aman!

You my friend are an ACE. Thanks Rene!

Thank you so much for this clear explanation

Hello Rene, In these days, I’m reading Eigrp from “Routing TCp/ip ver 1” and from
the new guide for ccie ver 5…
Now i cant’t able to anderstand the discuss of Fd…
If I do show ip eigrp topology (-all link) …the first value is Fd,( in the bracket , they call
computed distance reported distance, and now they say which is not always true that a router, during a topology change, choose that we call feasible successor…
what is the real story??

Hi Francesco,

EIGRP will store all the possible paths in its topology table, between the brackets it stores the FD (feasible distance) and AD (advertised distance). For example:


156160 = feasible distance
128256 = advertised distance

Sometimes they use “computed distance” to refer to feasible distance and “reported” distance to refer to the advertised distance.

In the topology table you will find at least 1 successor and possible some feasible successors. To become a feasible successor, its AD has to be lower than the FD of the successor.

Hope this helps!



Hello Rene,
I Know, I know
the problem now is this:

 Jack#show ip eigrp topology 
P, 1 successors, FD is 156160
        via (156160/128256), FastEthernet0/0

I understand your explanation, is only that in the new guide they say about the value FD 156160 is an historical copy since a distance pass from active to passive.
This value is internal and never pass to neigbors, it could only decrease and is this that we check for FC…
they call (156160) first valure in the bracket …computed distance and this is that a router pass to neigbor…so they say that is not always true that if a router has more FS it chose that one meet the FC…

Hi Francesco,

I’m not sure I get your question exactly :slight_smile: What page in the CCIEv5 book do you refer to?


page 386 where they discuss about FD and 393 where they say about fs successor over successor :slight_smile:

Hi Francesco,

I just took a look and now I get what you are referring to :slight_smile: This is interesting, the FD is indeed a historical copy while the CD is not. I’ll write a post on this.



Wow… I’'wait for it…thanks :slight_smile:

Hi Rene,

I have three questions :-
1 - When Suddenly an route entry goes down the code for this entry will be Query or Active first ?
2 - When the route will become in update state ? do you mean it will become in update state when there is a change in the topology and it will become in update state till receiving ACK ? or when receiving an update for an entry so it will become in update state and in this case how long it will take for come back into passive state ? I’m really confused at this point ?
3 - When the route will become in reply state ? I have no Idea at this point ?